From 8eea06286f43385d81a2a6c56548690d92ae431c Mon Sep 17 00:00:00 2001
From: Christopher Haster <geky@geky.net>
Date: Sun, 17 Dec 2023 22:16:41 -0600
Subject: [PATCH] Added optionally crc32c calculation to dbgblock.py

This is useful for debugging checksum mismatches on disk.

And since dbgblock.py has some relatively flexible options for slicing
the disk, this can be used to find the checksum of any on-disk data
pretty easily.
---
 scripts/dbgblock.py | 21 ++++++++++++++++++++-
 1 file changed, 20 insertions(+), 1 deletion(-)

diff --git a/scripts/dbgblock.py b/scripts/dbgblock.py
index 9bee9d75..9329dd24 100755
--- a/scripts/dbgblock.py
+++ b/scripts/dbgblock.py
@@ -73,11 +73,20 @@ def xxd(data, width=16):
                 b if b >= ' ' and b <= '~' else '.'
                 for b in map(chr, data[i:i+width])))
 
+def crc32c(data, crc=0):
+    crc ^= 0xffffffff
+    for b in data:
+        crc ^= b
+        for j in range(8):
+            crc = (crc >> 1) ^ ((crc & 1) * 0x82f63b78)
+    return 0xffffffff ^ crc
+
 def main(disk, block=None, *,
         block_size=None,
         block_count=None,
         off=None,
-        size=None):
+        size=None,
+        cksum=False):
     # is bd geometry specified?
     if isinstance(block_size, tuple):
         block_size, block_count_ = block_size
@@ -115,6 +124,7 @@ def main(disk, block=None, *,
                 else off[1] - off[0] if isinstance(off, tuple) and len(off) > 1
                 else block_size)
 
+        # print the header
         print('block %s, size %d' % (
             '0x%x.%x' % (block, off)
                 if off is not None
@@ -129,6 +139,11 @@ def main(disk, block=None, *,
         for o, line in enumerate(xxd(data)):
             print('%08x: %s' % ((off or 0) + 16*o, line))
 
+        # render the checksum if requested
+        if cksum:
+            cksum = crc32c(data)
+            print('%8s: %08x' % ('crc32c', cksum))
+
 if __name__ == "__main__":
     import argparse
     import sys
@@ -163,6 +178,10 @@ if __name__ == "__main__":
             int(x, 0) if x.strip() else None
             for x in x.split(',')),
         help="Show this many bytes, may be a range.")
+    parser.add_argument(
+        '-x', '--cksum', '--crc32c',
+        action='store_true',
+        help="Calculate and show the crc32c of the data.")
     sys.exit(main(**{k: v
         for k, v in vars(parser.parse_intermixed_args()).items()
         if v is not None}))